Aerofoils (airfoils) are structures that generate aerodynamic forces when traveling through a fluid such as water or air. These structures are commonly found on vehicles that are designed to move at high speed, such as airplanes, helicopters, race cars and boats.
When moving through a fluid, aerofoils generate lift, which is the force that is perpendicular to the direction of motion. The direction and amplitude of the lift is controlled by the angle of attack and shape of the aerofoil. The aerofoil deflects incoming air, resulting in a force that is in the direction that is generally opposite to the deflection (the force component parallel to the direction of motion is called drag).
For use on airplanes, aerofoils are produced from material that ideally has properties of strength, elasticity, low weight and corrosion resistance. Commonly, airplane aerofoils are made from metals or metal alloys.
More recently, aerofoils are produced from composite materials, since those combine advantageous properties of being very strong and corrosion resistant, yet having low weight. In general, composite materials consist of a combination of materials that are mixed together to form a structure (composite) that has specific structural properties. The combined materials in the structure do not merge or dissolve in the structure; rather, the individual components act in a synergetic fashion in the final structure. Composite materials usually contain a fibrous material that is embedded in a resin matrix. Load on the material will be transferred to the fibers by the surrounding matrix. The strength and stiffness of the material will in turn depend on the orientation and stacking of the fibers. A unidirectional material will have fibers that all run in the same direction, while fibers in a bidirectional material typically run in directions that are 90° apart, i.e. they are perpendicular to one another.
Aerofoils are typically produced in parts, i.e. parts of the aerofoil are produced independently and the individual parts joined together to form the final structure. The disadvantage of such production methods is that there will be joints where the parts meet, and such joints may have irregularities, which leads to suboptimal aerodynamic properties of the aerofoil. Further, the strength of the aerofoil can be compromised when it is manufactured in parts.
For example, aerofoils that are used in race cars are typically manufactured as two main components that are joined together to form the aerofoil. Usually, there are two molds used in such production, an upper mold and a lower mold. The molds will usually meet at the upper or lower side of the aerofoil, rather than at its leading edge, to avoid having a joint at the leading edge which is both structurally critical and could lead to greatly diminished aerodynamic properties of the aerofoil.
Yet, the final molded and glued aerofoil will need substantial post-production to smoothen out any rough edges that may have formed at the joint of the two (or more) parts. While it is possible to apply coating to the final structure to smoothen out any irregularities and improve its aerodynamic properties, such post-production has the disadvantages that it increases cost of production and also results in increased weight of the product. Particularly in race cars, such increased weight is to be avoided.